Do school based food and nutrition policies improve diet and reduce obesity?

Jaime PC, Lock K

CRD summary

The review concluded that nutrition guidelines and price interventions were effective in improving school food environments and dietary intake There were few studies that evaluated the impact of school food policies on body mass index. The authors' conclusions should be interpreted with caution due to methodological limitations in the review.

Authors' objectives

To assess the effectiveness of school food and nutrition policies in improving the school food environment, student's dietary intake and decreasing overweight and obesity.

Searching

PubMed, CAB Abstracts, Web of Knowledge, LILACS and The Cochrane Library were searched from inception to November 2007; search terms were reported. Internet searches were carried out and experts in the field were contacted to identify unpublished or missing studies. References lists of included studies and relevant reviews were searched.

Study selection

Controlled and uncontrolled trials of food or nutrition policies that involved changes in the school food environment in preschools and primary and secondary schools and that evaluated menu composition, availability of food and drink, dietary intake or body mass index (BMI) were eligible for inclusion. Cross-sectional studies (with a non-exposed comparison group) carried out after implementation of the intervention were eligible. Studies that targeted students with a specific medical problem were excluded.

Most studies were of nutrition guidelines (most were modifications of school food services) or price interventions (most offered free or reduced-price healthy food) in a broad age range of populations. Most control groups received no relevant intervention exposure. Commonly used outcomes included consumption of energy (or total fat) and consumption of fruit and vegetables. Most studies were conducted in USA or UK.

Abstracts were screened by one reviewer and full papers were screened by two reviewers (who then agreed on final inclusion).

Assessment of study quality

The authors did not state that they assessed study quality.

Data extraction

The authors did not state how many reviewers extracted data.

Methods of synthesis

A narrative synthesis was conducted, grouped by type of nutrition policy.

Results of the review

Eighteen studies were included in the review: 11 randomised controlled trials; four non-randomised non-controlled trials; two non-randomised controlled trials; and one cross-sectional study). Where stated, sample sizes ranged from 135 to 5,106 children.

Nutrition guidelines (nine studies): Three of four studies found that intervention schools had a significant reduction in total and saturated fat on school menus; one study found no difference in total and saturated fat. Four studies showed that intervention guidelines led to increased fruit and vegetable availability. Three studies reported significant decreases of total fat and saturated fat intake from use of guidelines and two studies reported increases in fruit and vegetable intake. The one study that evaluated impact on body mass index found no difference between groups after one year of follow-up.

Price interventions (eight studies): Two studies reported significant increases in low fat snacks and fruit and vegetable sales following price reductions. Four studies that offered fruit and vegetables for free (or by subsidised subscription) showed statistically significant increases in fruit consumption either during or after the programmes.

Regulation of food and drink availability (two studies): Both studies used a restrictive nutrition policy to limit access to unhealthy foods and both suggested the policy was associated with significant, but limited, reductions in unhealthy food sales.

Authors' conclusions

Nutrition guidelines and price interventions were effective in improving school food environments and dietary intake. Few studies evaluated the impact of school food policies on body mass index.

CRD commentary

The review addressed a clear question supported by appropriate eligibility criteria. Several methods were used to conduct a broad search for published and unpublished studies. It was unclear whether the authors used language restrictions. Study abstracts were screened by only one reviewer and no details were provided on how data was extracted, so the possibility that reviewer error and bias affected the review processes could not be ruled out. No assessment of study quality was made, which made it very difficult to assess the reliability of the included studies. Use of a narrative synthesis was appropriate as the authors reported marked heterogeneity in interventions and outcomes. In light of certain key limitations in the review methodology the authors' conclusions should be interpreted with caution.

Implications of the review for practice and research

Practice: The authors did not state any implications for practice.

Research: The authors stated a need for research to evaluate the effect of school nutrition policies on childhood obesity, with particular focus on which were most effective and cost-effective. The authors stated a need for research on which school policies could tackle the influence of the food industry in school environments.

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.